In the most common example, persons who live, go to school or work in a building and who are immediately caught in an Active Shooter event are typically fleeing for their lives, and those outside the danger area in other parts of the building may not know for some time of the ongoing danger. There is usually no electronic alert system or automated voice system in a building to warn building occupants of a potential Active Shooter event as there is for a building fire alarm. In public schools, the administration will make a loud speaker announcement if it is under attack and in colleges, a campus wide alert system will be activated at a point someone can make an emergency 911 call. Active shooter statistics show that these alerts often occur two or more minutes after the incident begins. A campus wide texting system may activate several minutes after the official alert notified the police.
Many people may be shot before a 911 call is received and the 911 operator will try and get information about the shooter(s) and their location(s). There will be a number of 911 calls coming from the incident scene, but in the next 2-3 minutes police most likely will not have a suspect description, the number of shooter(s), or the location of the shooter(s). When police arrive on scene they will form building entry teams and the senior officer on the scene will assume incident command and continue to be in communication with the 911 police dispatch officer for any information coming from individuals trapped in the building.
Once on site, building entry teams (BETs) enter the building and move in different directions in search of the shooter(s) and the location(s) of victim(s) while simultaneously seeking useful on-site information. At this time, BETs generally don't have a subject description. Police often seek information from victims while assisting victims to safety. Once they finally pinpoint a last location and possibly a description of the shooter(s), police continue searching the building. They listen for gunfire to alert them of the shooter's general location. The building entry teams generally do not have any knowledge of the interior building space other than their building reference system of A side (street side), then clockwise B side, C side and D side of the building. Building entry teams only have their radios to try and coordinate their location and movement. Unless they can orient on gunfire they don't know where the shooter(s) are or if they are still in the building.
The Incident Commander has little if any ability for a proactive command as he is dependent on the building entry teams for real-time intelligence. He may or may not have building floor plans to familiarize him with the building or to plot the locations of his teams in the building. Law enforcement understands that the quicker they can close with the shooter the quicker they will stop the killing. Unfortunately, in today's environment their movement in the building is a time consuming extensive search for the suspect(s) unless the team happens to luck out through gunfire echo's and receipt of timely intelligence from victims calling for help on a cell phone. In such an environment, where an Active Shooter is not contained and multiple police teams are in the building, command and control is difficult and friendly fire is always a concern as all fingers are on triggers.